Dating

Why would he joke about this?

My boyfriend jokes about have a std early last month. I can't remember the exact day but it was a long time ago but not too long. He was acting distant and barely replying to me. He would randomly hit me up days apart laughing and joking saying he had a std. He did it twice on different days and both times he said it was a joke. He told me to get tested but I got very angry. Then told me it was joke and didn't feel like arguing. He said he knows how I get when im very angry and said he didn't feel arguing but it was a joke. Fast forward to a few days ago I began having pains and having to pee a lot. I told my boyfriend the problems I had but he said it was just a uti. When we got off the phone, he kept joking and saying that I had stds. So i told him what day i was going to the doctor and he replied with ok. On that day i was going to the doctor he didn't reply to me. This day i got told i had a std and got a shot the same day. I called and called and he didn't answer until later that day. I told him what happened and he wouldn't believe me. He did say he was too scared to go to the doctor and didn't think he had it. He didn't say much but was denying he has it cause he has no symptoms.
Why would he joke about this?
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